As the on-vehicle batteries, secondary batteries have been widely known in which an electrode group is housed in a metal or resin container filled with an electrolyte solution. The electrode group includes a positive electrode sheet and a negative electrode sheet which are partitioned by a separator.
Typically, lithium ion secondary batteries have been known. The lithium ion secondary batteries include a wound type battery having a separator held between one positive electrode sheet and one negative electrode sheet, and a laminated type battery having positive electrode sheets and negative electrode sheets stacked on each other with a sheet-shaped separator held therebetween.
In particular, the laminated type battery has higher heat dissipation property than the wound type battery. In view of this, examinations have been conducted on the battery module formed by stacking a plurality of laminated type batteries that has smaller size and higher energy density and satisfies the requirements of higher capacity and higher output.
On the other hand, it has been known that the lithium ion secondary battery generates heat in the charging and discharging, and the battery performance thereof will change as the internal temperature changes. Therefore, in the battery module formed by stacking the plural laminated type batteries, the temperature varies in the unit cells in the center and on the outside in the stacking direction of the laminated type batteries. If the temperature variation is increased, the deterioration in the laminated type battery with higher temperature is promoted, resulting in the shorter lifetime of that laminated type battery. In view of this, in order to homogenize the burden on the batteries and facilitate the control, homogenizing the temperature has been a subject.
For this subject, PTL 1 has disclosed the technique for homogenizing the temperature of the laminated type batteries. According to PTL 1, the power storage cell having the exterior body housing the positive electrode, the negative electrode, and the electrolyte solution, and the heat dissipation plate formed on the outer surface of the exterior body are provided, wherein three or more layers of the power storage cells and the heat dissipation plates are alternately stacked and the thermal conductivity of the heat dissipation plate on the outside is smaller than that on the inside, so that the temperature difference between the power storage cells is reduced.